// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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package org.springframework.asm;

/**
 * The path to a type argument, wildcard bound, array element type, or static inner type within an
 * enclosing type.
 *
 * @author Eric Bruneton
 */
public final class TypePath
{

    /** A type path step that steps into the element type of an array type. See {@link #getStep}. */
    public static final int ARRAY_ELEMENT = 0;

    /** A type path step that steps into the nested type of a class type. See {@link #getStep}. */
    public static final int INNER_TYPE = 1;

    /** A type path step that steps into the bound of a wildcard type. See {@link #getStep}. */
    public static final int WILDCARD_BOUND = 2;

    /** A type path step that steps into a type argument of a generic type. See {@link #getStep}. */
    public static final int TYPE_ARGUMENT = 3;

    /**
     * The byte array where the 'type_path' structure - as defined in the Java Virtual Machine
     * Specification (JVMS) - corresponding to this TypePath is stored. The first byte of the
     * structure in this array is given by {@link #typePathOffset}.
     *
     * @see <a
     * href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.20.2">JVMS
     * 4.7.20.2</a>
     */
    private final byte[] typePathContainer;

    /** The offset of the first byte of the type_path JVMS structure in {@link #typePathContainer}. */
    private final int typePathOffset;

    /**
     * Constructs a new TypePath.
     *
     * @param typePathContainer a byte array containing a type_path JVMS structure.
     * @param typePathOffset    the offset of the first byte of the type_path structure in
     *                          typePathContainer.
     */
    TypePath(final byte[] typePathContainer, final int typePathOffset)
    {
        this.typePathContainer = typePathContainer;
        this.typePathOffset = typePathOffset;
    }

    /**
     * Converts a type path in string form, in the format used by {@link #toString()}, into a TypePath
     * object.
     *
     * @param typePath a type path in string form, in the format used by {@link #toString()}. May be
     *                 {@literal null} or empty.
     * @return the corresponding TypePath object, or {@literal null} if the path is empty.
     */
    public static TypePath fromString(final String typePath)
    {
        if (typePath == null || typePath.length() == 0)
        {
            return null;
        }
        int        typePathLength = typePath.length();
        ByteVector output         = new ByteVector(typePathLength);
        output.putByte(0);
        int typePathIndex = 0;
        while (typePathIndex < typePathLength)
        {
            char c = typePath.charAt(typePathIndex++);
            if (c == '[')
            {
                output.put11(ARRAY_ELEMENT, 0);
            }
            else if (c == '.')
            {
                output.put11(INNER_TYPE, 0);
            }
            else if (c == '*')
            {
                output.put11(WILDCARD_BOUND, 0);
            }
            else if (c >= '0' && c <= '9')
            {
                int typeArg = c - '0';
                while (typePathIndex < typePathLength)
                {
                    c = typePath.charAt(typePathIndex++);
                    if (c >= '0' && c <= '9')
                    {
                        typeArg = typeArg * 10 + c - '0';
                    }
                    else if (c == ';')
                    {
                        break;
                    }
                    else
                    {
                        throw new IllegalArgumentException();
                    }
                }
                output.put11(TYPE_ARGUMENT, typeArg);
            }
            else
            {
                throw new IllegalArgumentException();
            }
        }
        output.data[0] = (byte) (output.length / 2);
        return new TypePath(output.data, 0);
    }

    /**
     * Puts the type_path JVMS structure corresponding to the given TypePath into the given
     * ByteVector.
     *
     * @param typePath a TypePath instance, or {@literal null} for empty paths.
     * @param output   where the type path must be put.
     */
    static void put(final TypePath typePath, final ByteVector output)
    {
        if (typePath == null)
        {
            output.putByte(0);
        }
        else
        {
            int length = typePath.typePathContainer[typePath.typePathOffset] * 2 + 1;
            output.putByteArray(typePath.typePathContainer, typePath.typePathOffset, length);
        }
    }

    /**
     * Returns the length of this path, i.e. its number of steps.
     *
     * @return the length of this path.
     */
    public int getLength()
    {
        // path_length is stored in the first byte of a type_path.
        return typePathContainer[typePathOffset];
    }

    /**
     * Returns the value of the given step of this path.
     *
     * @param index an index between 0 and {@link #getLength()}, exclusive.
     * @return one of {@link #ARRAY_ELEMENT}, {@link #INNER_TYPE}, {@link #WILDCARD_BOUND}, or {@link
     * #TYPE_ARGUMENT}.
     */
    public int getStep(final int index)
    {
        // Returns the type_path_kind of the path element of the given index.
        return typePathContainer[typePathOffset + 2 * index + 1];
    }

    /**
     * Returns the index of the type argument that the given step is stepping into. This method should
     * only be used for steps whose value is {@link #TYPE_ARGUMENT}.
     *
     * @param index an index between 0 and {@link #getLength()}, exclusive.
     * @return the index of the type argument that the given step is stepping into.
     */
    public int getStepArgument(final int index)
    {
        // Returns the type_argument_index of the path element of the given index.
        return typePathContainer[typePathOffset + 2 * index + 2];
    }

    /**
     * Returns a string representation of this type path. {@link #ARRAY_ELEMENT} steps are represented
     * with '[', {@link #INNER_TYPE} steps with '.', {@link #WILDCARD_BOUND} steps with '*' and {@link
     * #TYPE_ARGUMENT} steps with their type argument index in decimal form followed by ';'.
     */
    @Override
    public String toString()
    {
        int           length = getLength();
        StringBuilder result = new StringBuilder(length * 2);
        for (int i = 0; i < length; ++i)
        {
            switch (getStep(i))
            {
                case ARRAY_ELEMENT:
                    result.append('[');
                    break;
                case INNER_TYPE:
                    result.append('.');
                    break;
                case WILDCARD_BOUND:
                    result.append('*');
                    break;
                case TYPE_ARGUMENT:
                    result.append(getStepArgument(i)).append(';');
                    break;
                default:
                    throw new AssertionError();
            }
        }
        return result.toString();
    }
}
